Question

Find the sum of the first 10 terms 40, 37, 34, 31

Answer 1

Solution :-

Firstly finding common difference of the series

As we know that

• Common difference ( d ) = t₂ - t₁

→ Common difference = 37 - 40

→ Common difference = - 3

Now, as we know that

• Sn ( Sum of n terms ) = n/2 [ 2a + ( n - 1 ) d ]

Substituting n = 1. Since the sum of no. of terms is 10 . And substituting a = 40 ,since first term is 40

=> S₁₀ = 10/2 [ 2(40) + ( 10 - 1 ) -3 ]

=> S₁₀ = 5 [ 80 - 27 ]

=> S₁₀ = 5 × 53

=> S₁₀ = 265

Hence , sum of first 10 terms ( S₁₀ ) = 265